1. Technical Field
The present invention relates to USB control systems, and more particularly, to an apparatus and method for controlling a power-saving (suspending) mode in a USB control system, reducing current consumption by suspending the power supplied to internal blocks during the suspending mode.
2. Discussion of Related Art
The Universal Serial Bus (USB) was developed for purpose of regularizing interface protocols to connect personal computers with peripheral devices such as mice, printers, modems, speakers, and so forth. USB functions as a kind of serial port. USB was proposed by a consortium of PC manufacturers including Intel, Compaq, Microsoft, Philips, IBM, and NEC.
The USB specification makes it possible to communicate with a peripheral device of a computer or hosting system without needing complicated adaptors for peripheral devices. Many hosting systems, e.g., personal computers, are equipped with a USB post as a standard serial port.
A data rate of a conventional serial port is not over 100 Kbps (kilobits per second). A data rate of a typical USB is 127 Mbps (megabits per second). Thus, the USB is able to provide a relatively high-speed data transmission environment for peripheral devices connected thereto. In addition, the USB is capable of connecting up to 127 devices in a chain. Further, a peripheral device cooperated with the host through the USB is operable without an additional power supply. As the USB is available for simultaneously use by a plurality of peripheral devices on the same interconnection without specifically establishing software or hardware connections between a host and the peripheral devices, a smaller number of ports may be used, convenient system installation is enabled, portable devices including a USB may be made small, and so on.
An apparatus for conducting an interfacing operation with a host such as a personal computer by way of the USB may be called a USB device. The USB device may have a USB controller for operating functions needed from the host. For USB devices used in portable applications, power consumption becomes an important issue. Therefore, many USB controllers are forced into a power-saving mode (e.g., a suspending mode) when there is no operation request from the host during active modes thereof, reducing unneeded power consumption.
FIG. 1 is a block diagram of a USB control system 100.
Referring to FIG. 1, the USB control system 100 comprises a host 120 and a USB controller for performing instructions requested from the host 120.
The USB controller includes a voltage controller 110, a physical layer (PHY) unit 130, a link unit 140, and a micro-control unit (MCU) 150. The PHY unit 130 includes a PHY analog block 131 and a PHY digital block 133. The PHY analog block 131 includes an input/output block 135 and a phase-locked loop (PLL) 137.
The voltage controller 110 receives an external voltage EXT_VDD and a reference voltage VREF, and generates an internal voltage INT_VDD. The blocks within the USB controller are operable using the internal voltage INT_VDD as a voltage source. If there is an operation request from the host 120, the input/output block 135 transfers the received operation request, e.g., received data, to the PHY digital block 133 in synchronization with a clock signal CLK generated from the PLL 137. The PHY digital block 133 decodes the transferred data to abstract effective data and transfers the abstracted effective data to the MCU 150. The MCU 150 executes an operation for analyzing the request of the host 120 in accordance with the effective data.
If there is no operation request from the host 120 during a predetermined time, the USB controller is put into the suspending mode, reducing current consumption therein. In the suspending mode, the input/output block 135 is deactivated and the PLL 137 stops generating the clock signal CLK. Without the supply of the clock signal CLK, the PHY digital block 133 and the link unit 140, being composed of pure digital logic circuits, are deactivated, reducing current consumption therein. Further, the MCU 150 detects the suspending mode through an interrupt condition and is put into the suspending mode by itself.
However, the USB controller shown in FIG. 1 enables a leakage current to flow there through, wherein the internal voltage INT_VDD is supplied to all the internal circuit blocks or units. As a result, power consumption continues in the suspending mode and a current level may exceed a maximum current level defined in the USB Specification.
Therefore, a need exists for an apparatus and method for controlling a power-saving mode in a USB control system.